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| United States Patent |
5,302,649
|
|
Sasaki
, et al.
|
April 12, 1994
|
Curable film forming compositions
Abstract
There are provided a pressure-sensitive adhesive and other compositions
which free radical cured mixtures in which a halogenated hydrocarbon was
present during free radical cure, of at least one unsaturated elastomeric
polymer and at least one organic additive which is substantially
nonresponsive to the action of free radicals and present in an amount
sufficient to modify the properties of the cured elastomeric polymer.
| Inventors:
|
Sasaki; Yukihiko (Claremont, CA);
Lossner; Kevin (Monrovia, CA)
|
| Assignee:
|
Avery Dennison Corporation (Pasadena, CA)
|
| Appl. No.:
|
452563 |
| Filed:
|
December 14, 1989 |
| Current U.S. Class: |
524/274; 428/355BL; 522/110; 524/271; 524/272; 524/276; 524/483; 524/484; 524/486; 524/505; 524/534; 525/98; 525/193; 525/194 |
| Intern'l Class: |
C08L 053/00 |
| Field of Search: |
524/272,274,271,483,484,486,505,276,534
525/98,193,194
428/355
522/110
|
References Cited
U.S. Patent Documents
| 4243500 | Jan., 1981 | Glennon | 524/272.
|
| 4556464 | Dec., 1985 | St. Clair | 524/271.
|
| 4948825 | Aug., 1990 | Sasaki | 524/274.
|
Primary Examiner: Kight, III; John
Assistant Examiner: Cooney, Jr.; John M.
Attorney, Agent or Firm: Christie, Parker & Hale
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of and is entitled to the benefit of the
filing date of U.S. patent application Ser. No. 07/057,504, filed Jun. 3,
1987, now U.S. Pat. No. 4,948,825, incorporated herein by reference.
Claims
What is claimed is:
1. A pressure-sensitive adhesive comprising a free radical cured mixture of
at least one unsaturated elastomeric polymer present in a total amount of
from about 10 to about 60 parts by weight of the mixture and at least one
organic additive which is substantially nonresponsive to the action of
free radicals, said organic additive selected from the group consisting of
aromatic organic additives which are at least 50% saturated and aliphatic
organic hydrocarbon additives in which at least 65% of the unsaturated
groups of the hydrocarbon as formed are saturated, the total of organic
additive being present in an amount of from about 90 to about 40 parts by
weight of the mixture, said cured adhesive having a glass transition
temperature at least 10.degree. C. below use temperature and an elevated
temperature shear higher than the elevated temperature shear prior to
cure, and in which a crosslinking agent comprising a brominated
hydrocarbon is present during free radical cure of the mixture.
2. A pressure-sensitive adhesive as claimed in claim 1 wherein said
brominated hydrocarbon is at least one compound selected from the group
consisting of hexabromocyclododecane and
1,2-dibromoethyl-3,4-dibromocyclohexane.
3. A pressure-sensitive adhesive as claimed in claim 1 in which the organic
additive is present in a concentration of about 45 to about 85 percent by
weight based on the weight of the elastomeric polymer and organic
additive.
4. A pressure-sensitive adhesive as claimed in claim 1 in which the
unsaturated elastomeric polymer is selected from the group consisting of
styrene-butadiene block copolymers, styrene-butadiene-styrene block
copolymers, styrene-isoprene block copolymers, styrene-isoprene-styrene
block copolymers, multiarmed-styrene-isoprene block copolymers,
polybutadiene, polyisoprene and mixtures thereof.
5. A pressure-sensitive adhesive as claimed in claim 3 in which the
unsaturated elastomeric polymer is selected from the group consisting of
styrene-butadiene block copolymers, styrene-butadiene-styrene block
copolymers, styrene-isoprene block copolymers, styrene-isoprene-styrene
block copolymers, mulitarmed-styrene-isoprene block copolymers,
polybutadiene, polyisoprene and mixtures thereof.
6. A pressure-sensitive adhesive as claimed in claim 1 in which the organic
additive is selected from the group consisting of saturated aliphatic
resins, saturated aromatic resins, saturated oils and mixtures thereof.
7. A pressure-sensitive adhesive as claimed in claim 5 in which the organic
additive is selected from the group consisting of saturated aliphatic
resins, saturated aromatic resins, saturated oils and mixtures thereof.
8. A pressure-sensitive adhesive as claimed in claim 4 in which the organic
additive is selected from the group consisting of saturated aliphatic
resins, saturated aromatic resins, saturated oils and mixtures thereof.
9. A pressure-sensitive adhesive as claimed in claim 1 in which the
unsaturated elastomeric polymer is selected from the group consisting of
ABA block copolymers; multiarmed (AB).sub.x block copolymers and mixtures
thereof, wherein A is a block comprising at least one monoalkenyl arene, B
is an elastomeric conjugated diene block and x has a value greater than 2.
10. A pressure-sensitive adhesive as claimed in claim 3 in which the
unsaturated elastomeric polymer is selected from the group consisting of
ABA block copolymers; multiarmed (AB).sub.x block copolymers and mixtures
thereof, wherein A is a block comprising at least one monoalkenyl arene, B
is an elastomeric conjugated diene block and x has a value greater than 2.
11. A pressure-sensitive adhesive as claimed in claim 9 in which the
organic additive is selected from the group consisting of saturated
aliphatic resins, saturated aromatic resins, saturated oils and mixtures
thereof.
12. A pressure-sensitive adhesive which comprises a free radical cured
product of a mixture comprising, based on the weight of the mixture, from
about 15 to about 60 parts by weight of an unsaturated elastomer polymer
component, from about 85 to about 40 parts by weight of a tackifying
organic additive which is selected from the group consisting of saturated
aliphatic resins, saturated aromatic resins, saturated oils and mixtures
thereof, and an effective amount of a brominated hydrocarbon crosslinking
agent, present in an amount up to 10 parts by weight, said cured
pressure-sensitive adhesive having a higher elevated temperature shear as
compared to the mixture prior to cure and a glass transition temperature
of at least 10.degree. C. below use temperature.
13. A pressure-sensitive adhesive according to claim 12 wherein said
brominated hydrocarbon is at least one compound selected from the group
consisting of hexabromocyclododecane and 1,2-dibromoethyl-3,
4-dibromocyclohexane.
14. A pressure-sensitive adhesive as claimed in claim 12 in which the
unsaturated elastomeric polymer component comprises at least one
unsaturated elastomeric copolymer selected from the group consisting of
styrene-butadiene block copolymers, styrene-butadiene-styrene block
copolymers, styrene-isoprene block copolymers, styrene-isoprene-styrene
block copolymers, multi-armed styrene-isoprene block copolymers,
polybutadiene, polyisoprene and mixtures thereof.
15. A pressure-sensitive adhesive comprising a free radical cured mixture
comprising from about 15 to about 55 parts by weight of an unsaturated
styrene-isoprene-styrene block copolymer and from about 85 to about 45
parts by weight tackifying organic additive selected from the group
consisting of saturated aromatic resins, saturated aliphatic resins,
saturated oils and mixtures thereof, said pressure-sensitive adhesive
having a higher elevated temperature shear as compared to the mixture
prior to cure and a glass transition temperature at least 10.degree. C.
below use temperature, and in which a brominated hydrocarbon crosslinking
agent was present during free radical cure of the mixture.
16. A pressure-sensitive adhesive as claimed in claim 14 in which is
present prior to cure an end block reinforcing agent which is compatible
with the styrene blocks.
17. A pressure-sensitive adhesive according to claim 16 wherein said
brominated hydrocarbon is at least one compound selected from the group
consisting of hexabromocyclododecane and
1,2-dibromoethyl-3,4-dibromocyclohexane.
18. A pressure-sensitive adhesive comprising a free radical cured mixture
comprising, based on the weight of the mixture, from 15 to about 55
percent by weight of the mixture a multiarmed styrene-isoprene block
copolymer and from about 45 to about 85 percent by weight of the mixture
of an organic additive which is selected from the group consisting of
saturated aromatic resins, saturated aliphatic resins and mixtures
thereof, said pressure-sensitive adhesive having a high elevated
temperature shear as compared to the mixture prior to cure and a glass
transition temperature of at least 10.degree. C. below use temperature,
and in which a brominated hydrocarbon crosslinking agent was present
during free radical cure of the mixture.
19. A pressure-sensitive adhesive as claimed in claim 18 in which is
present prior to cure an end block reinforcing agent which is compatible
with the styrene blocks.
20. A pressure-sensitive adhesive comprising a free radical cured mixture
in which a brominated hydrocarbon was present during free radical cure of
the mixture comprising, based on the weight of the mixture, from 15 to
about 55 percent by weight of a styrene-butadiene-styrene block copolymer
and from about 45 to about 85 percent by weight of an organic additive
which is selected from the group consisting of aromatic resins and
mixtures thereof with saturated aromatic, saturated aliphatic and
saturated oils, said pressure-sensitive adhesive having a high elevated
temperature shear as compared to the mixture prior to cure and a glass
transition temperature of at least 10.degree. C. below use temperature.
21. A pressure-sensitive adhesive as claimed in claim 20 in which is
present prior to cure an end block reinforcing agent which is compatible
with the styrene blocks.
Description
BACKGROUND OF THE INVENTION
This invention is directed to reducing the energy required to improve the
properties of multicomponent polymer systems which form pressure-sensitive
adhesives.
More particularly, the invention is related to the use of halogenated
crosslinking agents for radiation (EB & UV) curing of adhesives containing
unsaturated elastomeric polymers, such as unsaturated block copolymers,
especially, though not limited to, styrene-isoprene block copolymers,
e.g., linear SI, SIS, multi-armed (SI).sub.x. Halogenated materials
significantly enhance the facility of free-radical materials crosslinking
of pressure-sensitive adhesive formulations containing unsaturated
elastomers, leading, at lower levels of free-radical generating energy, to
a higher degree of crosslinking, which is manifested by the formation of
more insoluble gel, lower swelling ratios, and significant improvements in
adhesive performance at elevated temperatures.
Conventional crosslinking systems for such adhesives have been based upon
the use of polyfunctional acrylates or methacrylates. Polythiols have also
been effectively used. These materials exhibit a number of disadvantages:
for example; curing may cause a considerable loss of peel and tack, and
the thermal instability of the crosslinkers requires in-line static mixing
immediately prior to coating for hot melt processes. Many of the
halogenated materials, in contrast, are thermally stable and are ideally
suited to hot melt (100% solids) processing, although they may also be
used in solution or emulsion processes.
Properties of unsaturated pressure sensitive adhesive compositions can be
improved by use of actinic radiation, such as ultraviolet (UV) radiation;
electron beam (EB) radiation. Normally, the adhesive is applied to
facestock and/or a release liner and subjected to a suitable curing action
to improve such properties as elevated temperature shear.
One means of cure is electron beam (EB) radiation. While the facestock
and/or release liner can sustain electron beam dosages up to a certain
level, e.g., 80 to 100 kiloGray (kGy), going beyond that level can result
in degradation of components of adhesive label and tape constructions such
as the face stock and/or release liner and/or adverse reactions between
the adhesive and the silicon release agent of the release liner.
Increased radiation requirements, whether EB or actinic, will reduce the
speed at which an adhesive coated substrate can pass under the radiating
surface or increase the number of radiating surfaces. Both are costly.
The present invention is directed to reducing the energy required to
achieve a positive modification in a pressure sensitive adhesive formed of
at least two components, one an unsaturated elastomeric polymer component,
the other an organic additive component which is one or more organic
additives which are at least dispersable in the elastomeric component.
Typically, the organic additive component is provided to tackify or
plasticize the elastomeric component.
SUMMARY OF THE INVENTION
According to the present invention, there are provided pressure-sensitive
adhesive compositions which comprise in combination at least one
unsaturated elastomeric polymer capable of undergoing gel forming
reactions in the presence of free radicals preferably generated by actinic
radiation or electron beam radiation, and at least one organic additive
normally a tackifier or plasticizer which is substantially nonresponsive
to free radicals and which are at least dispersable and preferably soluble
in the polymer and an effective amount of a halogenated crosslinking
agent. The elastomeric polymer preferably has a glass transition
temperature of from about -20.degree. to about -100.degree. C. The organic
additive affects a property of the pressure-sensitive adhesive
composition, such as tack or other properties. The improvement resides in
the use of a halogenated hydrocarbon crosslinker with organic additive
which is substantially nonresponsive to the action of free radicals, as
defined herein, to provide, upon cure, at reduced energy input, a
pressure-sensitive adhesive composition having a glass transition
temperature of at least 10.degree. C., preferably at least 20.degree. C.
below use temperature.
After cure, with the increase of gel content, the combination exhibits a
positive change in properties such as elevated temperature shear. This
occurs at substantially lower levels of free radical generation than would
have been required were the organic additive to consume a significant
amount of free radicals.
The present invention is directed to the use of a particular class of
organic additives; namely, halogenated hydrocarbons which reduce the
incipient gel dosage requirement for the compositions and provide, upon
cure, a pressure-sensitive adhesive composition where less actinic or
electron beam energy is required to initiate gel formation. The preferred
halogenated organic additions for the purposes of this invention are
chlorinated polyethylene and brominated hydrocarbons which are also fire
retardants and which have been found to be able to be successfully added
to SIS block copolymers to reduce incipient gel dosage. Specific examples
of thermally stable halogenated hydrocarbons are hexabromocyclododecane,
1,2-dibromoethyl-3,4-dibromocyclohexane, tetra bromo-bis-phenol A, bis
allyl ether, poly(tribromostyrene) and the like.
DETAILED DESCRIPTION
The present invention is directed to reducing the energy requirements of
free radical cross-linking of unsaturated polymers, preferably elastomeric
polymers which are part of multicomponent compositions such as
pressure-sensitive adhesives (PSA) in which the unsaturated polymers are
tackified or otherwise modified as to physical properties by addition of
at least one organic additive.
We have found that halogenated hydrocarbons enhance the free-radical
crosslinking of PSA formulations containing unsaturated polymeric
materials. Within the broad class of materials containing halogenated
functionality, a number of thermally stable compounds may be found which
are ideally suited for use in free-radical crosslinking agents of hot melt
pressure-sensitive adhesive formulations. Compatibility of these
substances with ordinary components of PSA formulae is variable; but
chlorinated polyethylene certain commercial fire-retardant chemicals have
been found to be particularly suitable for curing SIS, SI, SBS, and SB
based PSA's. The enhancement of cure has been demonstrated for both
ultraviolet (with and without photoinitiators) and electron beam
processes.
Properties of the pressure-sensitive adhesive composition are, in
accordance with the present invention, enhanced by free radical cure, with
free radicals preferably generated by electron beam (EB) radiation, or
actinic radiation, such as ultraviolet (UV) curing, with or without
photoinitiators and/or photosensitizers. The improvement resides in
utilizing as a property modifying additive, an organic additive which is
substantially nonresponsive to the action of free radicals in combination
with a halogenated hydrocarbon serving as a crosslinking agent to reduce
the energy required to achieve cure.
By the term "organic additive which is substantially nonresponsive to the
action of free radicals" (also organic additive herein) there is meant
saturated organic compounds and organic compounds which, when blended with
an unsaturated elastomeric polymer in proportions of about 40 parts by
weight of the unsaturated elastomeric polymer and 60 parts by weight
organic compound, will form a blend having a relative incipient gel
dosage, i.e. the ratio of incipient gel dosage of the blend to the
incipient gel dosage of the unsaturated elastomeric polymer, of no more
than about 1.85, preferably 1.65. The measurement is made for a blend
which is free of external cross-linking agents and for an EB radiation at
200 KV.
For electron beam radiation, incipient gel dosage is determined as a
minimum amount of electron beam (EB) dosage in kiloGray required to form a
toluene insoluble gel. Insoluble gel is measured by placing 200 milligrams
of a directly irradiated sample into 10 grams of toluene checking for the
presence of insoluble material after 24 hours standing. Radiation is
increased (or decreased) in increments of 10 kGy. If the solution appears
clear upon visual inspection it is filtered through qualitative filter
paper to check for the presence of gel. The procedure is repeated for each
10 kGy dosage level increment and the dosage at which gelation occurs is
interpolated from the data. If a gel was not observed, for example, at 60
kGy, but was at 70 kGy, the value of incipient gel dosage is reported as
65 kGy. In each instance, the sample is coated from a toluene solution
onto a release paper (50-75 g/m.sup.2) and dried in an oven. The sample
surface was directly exposed to EB radiation at 200 KV with inerting to
400 ppm O.sub.2 or less. For values reported herein, the EB unit used was
manufactured by Energy Sciences.
By the preferred use of organic additives which are substantially
nonresponsive to the action of free radicals, the energy required to
achieve a level of cross-linking within the unsaturated elastomeric
copolymer can remain unchanged and independent of organic additive
concentration.
The halogenated crosslinking agents also reduce incipient gel dosage but in
consequence of being free-radical generations. As such, they also reduce
the amount of external free energy required for cure.
Used with other organic additives which are substantially non-responsive to
the action of free radicals, the halogenated crosslinking agents of this
invention comprise thermally stable halogenated hydrocarbon, preferably
chlorinated polyolefins, chlorinated polyethylene, and bromonated
hydrocarbons. The presently preferred additives include 1,2-dibromo
ethyl-3,4-dibromocyclohexane; hexabromo-cyclododecane;
tetrabromo-bis-phenol A; bis (allyl ether); poly(tribromostyrene) and the
like.
For unsaturated compounds, saturation to a level sufficient to meet the
definition can be achieved by hydrogenation or otherwise eliminating
aromatic or aliphatic unsaturation with addition of groups which do not
consume free radicals. In the alternative, saturated or partially
hydrogenated organic compounds may be blended with saturated and/or highly
saturated organic additives to achieve the desired result, namely a
reduction of incipient dosage requirements to acceptable levels.
While not limiting, the invention will, for simplicity, be described in
terms of improving the properties of pressure-sensitive adhesives based on
unsaturated natural and synthetic elastomeric polymers including, but not
limited to, block, random or multiarmed copolymers and mixtures thereof.
Among the useful unsaturated elastomeric polymers there may, however, be
mentioned natural rubber, polybutadiene, polyisoprene, butyl rubber,
ethylene propylene diene rubbers, styrene-butadiene block copolymers,
styrene-butadiene-styrene block copolymers, styrene-isoprene block
copolymers, styrene-isoprene-styrene block copolymers, multiarmed
styrene-isoprene block copolymers and the like. Useful unsaturated
elastomeric polymers are also disclosed in U.S. Pat. No. 4,556,464 to St.
Clair incorporated herein by reference.
Preferably, the elastomeric block polymers to which the invention is
directed are ABA block or multiarmed (AB).sub.x block copolymers, wherein
x has a value of 2 or more and mixtures thereof and wherein A is a block
comprising at least one monoalkenyl arene, preferably styrene, alpha
methyl styrene, vinyl toluene and the like, and B is an elastomeric
conjugated diene block such as a polybutadiene or a polyisoprene block
with polyisoprene blocks preferred. More preferably, the elastomeric
copolymers are formed of styrene-butadiene-styrene block copolymers and/or
styrene-isoprene-styrene block, multiarmed styrene-isoprene block
copolymers, polybutadiene and polyisoprene. Mixtures of elastomers may be
employed.
Unsaturated elastomeric polymers forming the base resin of the invention
are or may be adapted to hot melt, solvent or emulsion coating. They are
preferably free radical cross-linked using actinic radiation, with or
without a photoinitiator, or by electron beam (EB) radiation. Cure is to
overcome the major deficiency of pressure-sensitive adhesives based on
unsaturated elastomeric polymers, namely, to have acceptable elevated
temperature cohesive strength. Crosslinking of the base polymer has been
used to enhance cohesive properties of the adhesives especially to improve
elevated temperature shear performance.
Thermal crosslinking during hot melt processing of unsaturated elastomeric
polymers may be achieved using the halogenated crosslinking agents of this
invention. The systems still, with precaution, may be benefited by the use
of external crosslinkers. Crosslinkers which are multifunctional monomers
such as acrylates and methacrylates are thermally reactive and the process
to achieve cure also requires in-line mixing to avoid premature
crosslinking independent of the ultimate means of cure. The same is true
of other crosslinking agents which are functional at much lower
concentrations. Polythiol crosslinkers, for instance, are functional at
concentrations of about 10% or less by weight of the total crosslinkers
used in the composition. The polythiol crosslinkers include for instance,
pentaerythritoltetrathioglycolate,
pentaerythritol-tetra(3-mercaptopropionate),
trimethylolethanetrimercaptopropionate,
trimethylolpropanetrithioglycolate, trimethylolpropane
tri(3-mercaptopropionate) and the like.
As with the multifunctional acrylates and methacrylates, the polythiol
cross-linkers are preferably added to the composition by in line mixing.
The purpose is to avoid premature crosslinking before cure the pressure
sensitive adhesive composition.
The unsaturated elastomeric base copolymers are not normally pressure
sensitive adhesives and pressure-sensitive adhesive properties are induced
by the addition of other hydrocarbon materials known as tackifiers. One
use of the organic additives of this invention is as a tackifier.
To avoid excess consumption of free radicals and the introduction of excess
energy into the system, any significant amount of hydrocarbon added to
modify the properties of the elastomeric resin is in the form of organic
additives which are substantially nonresponsive to free radicals. Their
inclusion does not substantially affect the ability to achieve improved
elevated temperatures properties such as shear by the action of the free
radicals and add their beneficial properties, e.g., tack to the cured
product.
As examples of organic additives which are substantially nonresponsive to
free radicals there may be mentioned hydrogenated organic compounds, such
as hydrogenated aromatic resins including hydrogenated polystyrene,
polyalpha-methyl styrene, polyvinyl toluene, copolymers of styrene with
other monomers and the like; hydrogenated aliphatic resins derived from
petroleum based products; highly hydrogenated rosins and rosin esters;
hydrogenated white oil, mineral oil and the like. As specific tackifiers
employed in the practice of the invention there may be mentioned
hydrogenated styrene based resins such as Regalrez.TM. resins designated
as 1018, 1033, 1065, 1078, 1094 and 1126 manufactured and sold by
Hercules, Inc.; Regalrez.TM. 6108 a 60% hydrogenated aromatic resin, also
manufactured by Hercules; hydrogenated C.sub.5 and/or C.sub.9 hydrocarbon
feed stocks such as Arkon.TM. P-70, P-90, P-100, P-125, P115, M-90, M-100,
M-110 and M-120 resins manufactured and sold by Arakawa Chemical and
Regalite.TM. R-100, MGB-63, MGB-67, MGB-70, resins manufactured and sold
by Hercules, Inc.; hydrogenated Polycyclo-pentadienes such as Escorez.TM.
5320, 5300 and 5380 resins manufactured and sold by Exxon Chemical,
hydrogenated polyterpene and other naturally occurring resins such as
Clearon.TM. P-105, P-115, P-125, M-105, M-115 manufactured and sold by
Yasuhara Yushi Kogyo Co. Ltd. of Japan and Eastotack.TM. H-100, H-115 and
H-130 resins manufactured and sold by Eastman chemical and the like;
Kaydol.TM. hydrogenated mineral oil manufactured and sold by Witco
Chemical and the like.
To be generally useful, organic aromatic additives should effectively be at
least 50% preferably at least 60% saturated and for the aliphatic
hydrocarbon at least 65% preferably 80% of unsaturated groups in the
product as formed should be saturated or otherwise rendered nonresponsive
to the action of free radicals. Complete saturation is preferred or at
least saturation to a level where upon inclusion into the elastomer there
will be a negligible additional consumption of free radicals over that
required to achieve the same level of cure by crosslinking of the
unsaturated elastomeric polymer. Some aromatic unsaturation is necessary
for compatibility with butadiene containing elastomers.
Organic additives which serve a tackifying function normally present in a
concentration ranging from about 40% to about 90% by weight, of mixture of
total, preferably from about 45% to about 85% by weight of the mixture of
unsaturated elastomeric polymers and tackifying organic additives.
Compositions containing less than about 40% by weight of an organic
additive typically do not have sufficient "quickstick" or initial grab and
compositions having too high a tackifying organic additive have too low a
cohesive strength even when cross-linked.
The compositions of the instant invention may be and normally are made up
of components (unsaturated elastomeric polymer and organic additives)
having multiple glass transition temperatures. To be functional as a
pressure sensitive adhesive the composition must have at least one glass
transition temperature at least about 10.degree. C. below use
temperatures, preferably at least 20.degree. C. below use temperatures.
As compared to ABA block copolymers, the presently preferred unsaturated
elastomeric polymers are multi-armed styrene isoprene block copolymers
having the formulas (SI).sub.x where x generally has a value greater than
2.
Linear styrene-isoprene (SI) and styrene-isoprene-styrene (SIS) block
copolymers do not perform as well as multi-armed (SI) polymers in forming
radiation-cured pressure sensitive adhesives at lower curing doses. This
problem may be solved by the use of organic additives of this invention
which, unlike most conventional tackifiers, do not consume an excessive
amount of radical during crosslinking thereby conserving cost and product
quality.
It has been found that high molecular weight styrene-isoprene multi-armed
block copolymers, alone or together with other elastomers, such as SB, SBS
and SIS when formulated with organic additives which are saturated,
hydrogenated tackifying resins give pressure sensitive adhesive formulae
which show superior ease of cure and when cured superior elevated
temperature shear properties. Properties after cure, match or surpass the
elevated temperature shear performance of any hot melt adhesives
commercially available.
Presently preferred formulation ranges for high performance
pressure-sensitive adhesives containing multiarmed (or radial)
styrene-isoprene block copolymers are on a by weight basis as follows:
15-60 parts unsaturated elastomeric polymer(s)
85-40 parts tackifying organic additives
0-10 parts crosslinking agents
Antioxidants are added as required. In low concentrations, the multiarmed
block copolymers may be considered as an elastomeric crosslinking
additive.
Base unsaturated elastomeric polymers used were a mixture of linear
styrene-isoprene-styrene (SIS) and styrene-isoprene (SI) block copolymers
known as Kraton.TM. D-1107 and D-1111; styrene-butadiene-styrene (SBS)
block copolymers known as Kraton.TM. D-1101 and D-1102 and DX-1300 and
multi-armed (SI).sub.x block copolymer known as Kraton.TM. D-1320X.sup.1
all manufactured and sold by Shell Chemical Company and styrene-butadiene
block copolymer known as Solprene.TM. 1205 manufactured and sold by
Housemex, Inc. As representative of an unsatisfactory tackifying
unsaturated aliphatic resin there was used Escorez.TM. 1310, a petroleum
based hydrocarbon resin manufactured and sold by Exxon Chemical Company,
and Piccolite.TM. A-115, an alpha-pinene resin manufactured and sold by
Hercules, Inc. Foral-85, a well known hydrogenated rosin ester
manufactured and sold by Hercules, Inc. may be functional or nonfunctional
as an organic additive depending on the elastomer(s) it is combined with.
The organic additives which are used to illustrate the instant invention
are of the Escorez.TM. 5000 series. Also used to illustrate the practice
of the invention are Regalrez.TM. 6108, 1078 and 1000 series of resins.
Kaydol.TM. mineral oil was as a representation of hydrogenated oil. The
invention is primarily illustrated in respect of effect of unsaturation of
the organic compound, namely, a tackifier, on incipient or relative
incipient gel dosage (the incipient gel dosage of a mixture divided by the
incipient gel dosage of the elastomer) required to initiate gel formation
versus resin concentration in percent by weight. Incipient gel dosage is
measured as defined above. To establish product properties, the
formulation was coated from toluene onto a release paper (50 g/m.sup.2),
dried in an oven and laminated to a 50 micron thick polyester film. EB
radiation was through the polyester film. 180.degree. Peel in Newtons per
Meter (N/M) were determined using PSTC-1 at 20 minute dwell. Loop tack was
measured by forming a loop from a 1 inch by 8 inch strip, adhesive face
out, inserted in the jaws of an Instron tester and moving the loop at the
rate of 12 inches per minute onto a stainless steel panel, then removing
the strip at the rate of 12 inches per minute as soon as one square inch
of contact is made. The highest force required to remove the loop is
reported in N/M. Shear reported in Kiloseconds (K.S.) was for
0.5.times.0.5 inch overlap on a stainless steel panel at a 500 gram force
load.
.sup.1 Also known as TRW-6-1523 and DX-XL.
While the invention has been described in terms of pressure sensitive
adhesives, it embraces other cured compositions comprising a free radical
cured mixture of at least one unsaturated elastomeric polymer and at least
one organic additive which is substantially nonresponsive to the action of
free radicals and present in an amount sufficient to modify a physical
property of the elastomeric polymer.
The presently preferred system for using halogenated hydrocarbons and
radiation curing involves the use of styrene-isoprene block copolymers,
such as Kraton D-1107, D-1111, D-1320X, etc., in conjunction with
saturated, hydrogenated tackifying resins such as those found in, but not
limited to, the Regalrez 1000 and Escorez 5300 series. The range of
concentrations for such formulae might vary between 20 and 60% rubber and
40 to 80% tackifying resin, with up to 0 and about 10% halogenated
hydrocarbon in the formulae to serve as a tackifier. Formulae may also
include photoinitiators or thermal radical initiators such as benzoyl
peroxide or AIBN. Among the fire-retardant materials screened, those with
low melting points seem to exhibit the best compatibility and performance.
Brominated compounds are preferred over fluorinated or chlorinated,
because of the greater lability of the carbon-bromine bond with respect to
high energy radiation. The material which has shown the best performance
of all those screened to date is 1,2-dibromoethyl-3,4-dibromocyclohexane,
which is available from Ethyl Corp. under the trade name Saytex BCL-462.
A typical radiation-curable PSA formula might be described by the following
proportions:
35% Styrene-isoprene block copolymer
65% Hydrogenated tackifying resin
1-4 pph brominated hydrocarbons
(1-4 pph photoinitiators)
0.5-2 pph antioxidants
Examples of the present invention are shown in Tables 1-8. As can be seen,
halogenated hydrocarbons such as brominated hydrocarbon fire retardants,
can be successfully added to Kraton.TM. 1107 and reduce incipient gel
dosage.
TABLE 1
______________________________________
Incipient gel dose effects with Kraton D-1107
Kraton
BCL- Incipient Gel
D-1107
462 HBCDD BE-51 Pyrochek
(kGy)
______________________________________
control
-- -- -- -- 85 .+-. 5
98 2 -- -- -- 55 .+-. 5
light gel
95.2 4.8 -- -- -- 55 .+-. 5
87 13 -- -- -- 55 .+-. 5
95.2 -- 4.8 -- -- 65 .+-. 5
95.2 -- -- 4.8 -- 55 .+-. 5
95.2 -- -- -- 4.8 65 .+-. 5
______________________________________
BCL-462 = 1,2dibromoethyl-2,3-dibromocyclohexane (Ethyl)
HBCDD = hexabromocyclododecane (Great Lakes)
BE-51 = tetrabromobis-phenol A, bis(allyl eter) (Great Lakes)
Pyrochek = poly(tribromostyrene) (Pyrochek 68PB, Ferro)
TABLE 2
______________________________________
Incipient gel dose effects of chlorinated polyethylene
with Kraton D-1107 linear SIS rubber
Kraton
Regalrez CPE AO Incipient Gel
D-1107
1078 4211 330 DLTDP (kGy)
______________________________________
control
-- -- -- -- 95 .+-. 5
40 58 2 0.5 0.5 55 .+-. 5
40 56 4 0.5 0.5 55 .+-. 5
______________________________________
TABLE 3
______________________________________
Incipient gel dose effects with multiarmed (Si).sub.x
TRW- Escor- Regalrez BCL- Incipient
6-1523
ez 5300 1065 AO330 DLTDP 462 Gel (kGy)
______________________________________
pure -- -- -- -- -- 25 .+-. 5
rubber
30 31 39 0.5 0.5 3 5 .+-. 5
______________________________________
TABLE 4
__________________________________________________________________________
Incipient gel dose effects with SBS/SI based adhesives
I-406
DX-1300
Piccolyte A115
Shellflex 371
AO330
DLTDP
BLC-462
Incipient Gel (kGy)
__________________________________________________________________________
100
-- -- -- -- -- -- 250 .+-. 10
100
-- -- -- -- -- 5 155 .+-. 5
-- 40 50 10 0.8 0.8 -- 155 .+-. 5
-- 40 50 10 0.8 0.8 5 85 .+-. 5
-- 40 50 10 0.8 0.8 BE-51
75 .+-. 5
5
-- 40 50 10 0.8 0.8 BA-43
<=20
5
__________________________________________________________________________
I-406 = FID (US) adhesive consisting of Kraton D1101, Solprene 1205,
Piccolyte A115, Hercolyn D and AO 330.
BA-43 = Bisacrylate of bis(hydroxythylether) of tetrabromobis-phenol A
TABLE 5
__________________________________________________________________________
Effects of 1,2-dibromoethyl-3,4-dibromocyclohexane
on the adhesive properties of a Kraton D-1107 formulation
Basic formula for 131-21 A to D: 25 Kraton D-1107, 8.2 Escorez 5320, 66.8
Regalrez 1065,
0.5 Ethyl 330 and 0.5 Cyanox LTDP
Parts
EB 180.degree.
70.degree. C.
70.degree. C.
Formula
BCL-462
Dose (kGy)
Looptack (N/m)
Peel (N/m)
DySh (kPa)
ETS (ks)
__________________________________________________________________________
131-21A
0 0 4290 sf/c
2200 c
9.4 c 1 c
21A 0 70 3270 sf/c
2170 c
45.7 c 10 f/p
21B 2 70 4030 sf/c
2330 c
52.8 c 500+
21C 4 70 3770 sf/c
2200 c
76.4 f/p
3.3 f/p
21D 6 70 3670 sf/c
2170 47.2 c 2.5 c/f
__________________________________________________________________________
70.degree. C. DySh = dynamic shear test at 70.degree. C.; 0.2"/min
crosshead speed, 0.5" .times. 0.5" stainless steel facestock
70.degree. C. ETS = aluminum facestock 1" .times. 1", 1 kg load. Lower
values of formulae with high content of BCL462 may be due to overcure or
other effects.
TABLE 6
______________________________________
Quantitative gel yeilds (percent total sample) for Table 5
samples by the MGP method (THF solvent)
Formula BCL-462 50 kGy 70 kGy
______________________________________
131-21A 0 4.7 19.2
131-21B 2 12.3 18.6
131-21C 4 15.9 20.8
131-21D 6 18.1 18.8
______________________________________
TABLE 7
______________________________________
Quantitive gel yields for Kraton D-1107 and Regalrez 1065
(percent total sample) by the MGP method (THF solvent)
KrD-1107
R-1065 BCL-462 25 kGy 50 kGy
75 kGy
______________________________________
100 0 0 1.0 0.0 70.0
100 0 5 0.6 7.8 62.8
35 65 0 0.2 0.6 9.4
35 65 5 1.5 25.6 30.5
20 80 0 0.6 0.7 14.0
20 80 5 1.5 17.6 19.2
______________________________________
TABLE 8
______________________________________
Effects of 1,2-dibromoethyl-3,4-dibromocyclohexane on the SAFT
performance of a styrene-isoprene block copolymer adhesive
Kraton Kr R- R- BCL- Dose SAFT
D-1320X D-1111 1094 1033 462 (kGy) (.degree.C.)
______________________________________
25 10 54 11 0 70 126 .+-. 4
25 10 45 20 2 70 155 .+-. nc
______________________________________
In Table 1, a control composition is compared with Examples having varying
amounts of additions to "Krayton D-1107", as indicated, with the incipient
gel dose effects reported in the table.
The examples in Table 2 indicate the incipient gel dose effects of
chlorinated polyethylene with "Krayton D-1107" and examples in Tables 3
and 4 show the incipient gel dose effects in other systems.
Table 5 shows the effects of a preferred brominated hydrocarbon on the
adhesive properties of a "Kraton D-1107" formulation against a control
sample with o EB dose (kGy). The quantitative gel yields for the examples
in Table 5 are given in Table 6, including the control example.
Table 7 also provides quantitative gel yields for Krayton D-1107 and
Regalrez 1065 and the brominated hydrocarbon (BCL-462). As can be seen,
the examples with BCL-462 have higher EB dose values. Table 8 shows the
improved SAFT performance of the example with the brominated hydrocarbon.
The first sample does not constitute a true control, as the compounding and
coating method differed between the two samples and the resin mix was
slightly different for both. However, the differences would lead one to
expect lower SAFT for the second sample; thus, the effect of BCL-462
(1,2-dibromoethyl-3,4-dibromocyclohexane) is shown. More data with true
controls are in preparation.
Similar results may be expected for the cure response of other rubber based
materials which use other elastomers, such as butyl rubber, SBR, etc.
CONTROLS 1-4
The following study was performed to establish the effect of using
conventional tackifying resins to tackify elastomers on the electron beam
(EB) dosage required to achieve incipient gel formation as a function of
tackifier (resin) content. There was employed SIS elastomeric polymers
known as Kraton.TM. D-1107 (Control 1), SBS block copolymers Kraton.TM.
D-1101 (Control 2) and DX 1300 (Control 3) and Kraton.TM. D-1320X, a
multi-armed styrene-isoprene block copolymers (Control 4).
The study established, first of all, the base level of EB dosage necessary
to achieve a cohesive strength improvement as evidenced by gel formation
in the base elastomer, more particularly, where at least 10% of the
elastomer of adhesive composition formed an insoluble gel. Since
conventional elastomer based pressure-sensitive adhesives contain about
40-90% by weight added tackifying resins, this means that the typical
adhesive formulations required an EB dosage of 2-5 times higher than the
dosage required for the elastomer itself to achieve an incipient gel
formation when an unsaturated C-5 hydrocarbon Escorez.TM. 1310, (Controls
1 and 4) and Piccolite A-115 alpha-pinene (Controls 2 and 3) tackifiers
are used as the tackifying resins. The elastomer requiring the lowest
dosage was the multiarmed (SI).sub.x copolymer.
EXAMPLES 1 AND 2
To illustrate the invention there was used Regalrez.TM. 1033 an 100%
hydrogenated (saturated) aromatic resin manufactured by Hercules, Inc.
(Example 1) and Escorez.TM. E-5380, a saturated aliphatic hydrocarbon
manufactured by Exxon (Example 2). The comparison was Control 1. As can be
seen incipient dosage to gel increased in proportion to the amount of
unsaturated tackifying resin introduced to the rubber whereas the use of
the hydrogenated tackifiers causes the incipient dosage to remain the same
or in some instances reduced.
EXAMPLE 3 AND CONTROL 5
Using the same procedure as the previous Examples and Controls the effect
of a saturated tackifier , Escorez.TM. 5380, (Example 3) and an
unsaturated tackifier, Escorez.TM. 1310 (Control 5) have on the relative
incipient gel dosage required to achieve gel formation for a multi-armed
styrene-isoprene block copolymer (Kraton.TM.-D-1320X) was compared.
CONTROLS 6 AND 7 AND EXAMPLES 4 TO 7
Table 9 tabulates the improved high temperature properties induced to
Kraton.TM. D-1107 and Kraton.TM. D-1320X using as the saturated tackifier
Regalrez.TM. 1078. While 180.degree. peel remain essentially unchanged
there is dramatic improvement in elevated temperature shear.
TABLE 9
______________________________________
Component Parts
Cont 6 Ex 4 Ex 5 Cont 7
Ex 6 Ex 7
______________________________________
Kraton .TM. D-1107
35 35 35 -- -- --
Kraton .TM. D-1320X
-- -- -- 35 35 35
Regalrez .TM. 1078
65 65 65 65 65 65
Antioxidant 1 1 1 1 1 1
EB Dosage, kGy
0 75 100 0 75 100
180.degree. Peel at 23.degree. C.,
1490 1770 1460 1690 1220 1320
(N/M)
180.degree. Peel at 70.degree. C.,
350 440 310 320 390 320
(N/M)
Looptack, (N/M)
1490 2300 2350 1690 1220 1320
Shear at 70.degree. C., (K.S.)
1.1 4.4 7.2 0.15 7 17.8
______________________________________
CONTROL 8 AND EXAMPLES 8 AND 9
The relative incipient gel formation dosage for Kraton.TM. D-1107 using an
aromatic tackifier of different levels of unsaturation was compared. They
are manufactured and sold by Hercules, Inc., under the designation .sup.P
iccolastic.TM. A-50 (0% hydrogenated), Regalrez.TM. 3102 (30%
hydrogenated); Regalrez.TM. 6108 (60% hydrogenated) and Regalrez.TM. 1033
(100% hydrogenated). The higher the degree of hydrogenation the lower the
dosage required, for a given level of resin concentration, to form a gel.
This is important since a certain amount, usually 30-40% of the base
rubber, must be crosslinked to form a network in order to achieve a
significant improvement in physical properties.
CONTROLS 1 AND 9 AND EXAMPLE 6
As recognized, partially hydrogenated rosins have been used as premium
tackifier resins for a long time. One of the best is Foral 85 manufactured
by Hercules, Inc. According to information available from Hercules, Inc.,
it is about 60% hydrogenated. FIG. 5 establishes that for Kraton.TM.
D-1107, Foral 85 (Control 8) is on a comparative basis significantly
better than Escorez.TM. 1310 (Control 1) as a relatively low free radical
consumer but not as good as Example 6 where Regalrez.TM. 1033 a saturated
hydrocarbon was used as the tackifier.
CONTROLS 10 TO 15 AND EXAMPLES 10 TO 15
Endex.TM. 160 is an aromatic end-block reinforcing resin compatible with
the polystyrene phase of the block copolymer Kraton D-1107 but not
compatible with the elastomeric polyisoprene phase. It does not
substantially interfere with crosslinking in presence of an organic
additive (Table 10) or a blend thereof (Table 11), but synergistically
provided exceptionally high elevated temperature shear strength on EB
cure.
CONTROLS 16, 17 AND 18, EXAMPLES 16, 17 AND 18
The following is to show that a mixture of saturated tackifiers Escorez.TM.
5300 and Regalrez.TM. 1065 can be used to improve high temperature shear
performance of a multiarmed styrene-isoprene rubber Kraton.TM. D-1320X.
The formulations in parts by weight is shown in Table 10 and the adhesive
properties as a function of EB dosage in Table 13 wherein "ETS" means
elevated temperature shear in kiloseconds.
TABLE 10
______________________________________
Formula
Elastomer Escorez .TM. 5300
Regalrez .TM. 1065
______________________________________
1 30 11.7 58.3
2 30 30.9 39.1
3 40 44.2 15.8
______________________________________
TABLE 11
______________________________________
Cont Ex Cont Ex Cont Ex
10 10 11 11 12 12
______________________________________
Kraton D-1107,
40 40 40 40 40 40
parts
Regalrez 1078, parts
60 60 60 60 60 60
Endex 160, parts
-- -- 10 10 15 15
Antioxidant, parts
1 1 1 1 1 1
EB dosage (kGy)
0 75 0 75 0 75
180.degree. C. Peel, (N/M)
1110 1160 1350 1220 1190 1000
Looptack, (N/M)
1890 1880 2250 1860 1890 1540
70.degree. C. Shear (K.S.)
0.1 3.2 3.2 50.1 6.7 81.7
______________________________________
TABLE 12
______________________________________
Cont Ex Cont Ex Cont Ex
13 13 14 14 15 15
______________________________________
Kraton D-1107,
40 40 40 40 40 40
parts
Regalrez 1078, parts
40 40 40 40 40 40
Escorez 5320, parts
20 20 20 20 20 20
Endex 160, parts
0 0 10 10 15 15
Antioxidant, parts
1 1 1 1 1 1
EB dosage (kGy)
0 75 0 75 0 75
180.degree. Peel, (N/M)
1340 1300 1340 1430 1360 1260
Looptack, (N/M)
2170 2140 1570 1710 1540 770
70.degree. C. Shear, (K.S.)
6 60.3 69.1 807 51.4 854
______________________________________
TABLE 13
__________________________________________________________________________
Cont/Ex
FORMULA
EB DOSAGE(kGy)
LOOPTACK
180.degree. PEEL, RT
180.degree. PEEL, 70.degree.
ETS, 70.degree. C.
__________________________________________________________________________
Cont. 16
1 0 2550 1670 140 0.2
Ex. 16
1 75 2410 1620 190 9.9
Cont. 17
2 0 2570 1600 65 0.1
Ex. 17
2 75 1260 1520 265 25.2
Cont. 18
2 0 1950 1350 245 3.0
Ex. 18
3 75 1220 1240 280 218.2
__________________________________________________________________________
EXAMPLE 19
The multiarmed copolymer Kraton.TM. D-1320X has an incipient gel dosage of
25 kGy. A mixture of 30 parts of the multiarmed copolymer, 31 parts
Escorez.TM. 5300 and 39 parts Regalrez.TM. 1065 also required 25 kGy to
achieve incipient gel formation.
CONTROL 20 AND EXAMPLES 26-29
Control 20 and Examples 26-29 are for the combination of an SBS copolymer
Kraton.TM. D-1102 tackified with a mixture of Regalrez.TM. 6108 and Kadol
Oil a hydrogenated mineral oil in the presence of trimethylolpropane
tri(3-mercaptopropionate) as a multifunctional polythiol crosslinker. As
can be seen in Table 14, the combination gives on cure excellent elevated
temperature shear.
TABLE 14
______________________________________
Cont 15
Ex 26 Ex 27 Ex 28 Ex 29
______________________________________
Kraton D-1102
40 40 40 40 40
Regalrez 6108
50 50 50 50 50
Kaydol Oil
10 10 10 10 10
TMPTMP* 0 0.6 0.6 1 1
Antioxidant
1 1 1 1 1
EB dosage 0 20 50 20 50
(kGy)
180.degree. Peel,
1390 1180 1120 1130 1060
(N/M)
Looptack, 1750 1352 1770 1850 1110
(N/M)
70.degree. C. Shear,
1 2.3 120+***
11.8 120+***
(K.S.)**
______________________________________
*TMPTMP is trimethylolpropane tri(3mercaptopropionate)
**Weight is 1000 g and overlap area is 1 sq. in.
***No failure
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